Imaging devices, including charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) sensors have commonly been used in photo-imaging applications. A CMOS imager circuit includes a focal plane array of pixels, each one of the pixels including a photosensor, for example, a photogate, photoconductor or a photodiode for accumulating photo-generated charge in the specified portion of the substrate. Each pixel has a charge storage region, formed on or in the substrate, which is connected to the gate of an output transistor that is part of a readout circuit. The charge storage region may be constructed as a floating diffusion region. In some imager circuits, each pixel may include at least one electronic device such as a transistor for transferring charge from the photosensor to the storage region and one device, also typically a transistor, for resetting the storage region to a predetermined charge level prior to charge transference.
In a CMOS imager, the active elements of a pixel perform the functions of: (1) photon to charge conversion; (2) accumulation of image charge; (3) resetting the storage region to a known state; (4) transfer of charge to the storage region; (5) selection of a pixel for readout; and (6) output and amplification of signals representing pixel reset level and pixel charge. Photo charge may be amplified when it moves from the initial charge accumulation region to the storage region. The charge at the storage region is typically converted to a pixel output voltage by a source follower output transistor.
Exemplary CMOS imaging circuits, processing steps thereof, and detailed descriptions of the functions of various CMOS elements of an imaging circuit are described, for example, in U.S. Pat. Nos. 6,140,630; 6,376,868; 6,310,366; 6,326,652; 6,204,524; 6,333,205; and 6,852,591, all of which are assigned to Micron Technology, Inc. The disclosures of each of the foregoing are hereby incorporated by reference in their entirety.
Semiconductor photosensors whether for a CMOS, CCD or other semiconductor imager can be fabricated on a common semiconductor substrate to form a pixel array. Each photosensor is responsive to radiation to produce an output that is a measurement of the amount of received radiation. An input optical device, such as a microlens array and/or an optical color filter array, are typically placed in the optical input path of the input radiation to control or manipulate the radiation in order for the radiation to be properly received at the pixels of the pixel array and within a specified color wavelength range. There is desire and need for simplified and efficient method, apparatus and system to focus and color separate input radiation in an imager.